Dissolution of Gold and Silver with Ammonium Thiosulfate from Mangano-Argentiferous Ores Treated in Acid-Reductive Conditions

Significance Statement

Deposits of low-grade ore blended with silver and gold related to arsenic, manganese, iron and silica have been found.in nearly all metallurgical processes. Mangano-argentiferous, which is a manganese-silver compounds show a characteristics behavior. However, typical concentration approaches are normally inadequate for extracting an appreciable amount. Although, pyrometallurgical methods are an exceptional, casting is not preferable due to the fact that the process is costly and low grade minerals cannot meet the cost needed for this process.

Therefore, most researchers have focused on new methods for reducing its refractory attributes through the implementation of a number of treatments. In fact, sometimes most researchers opt to do a preliminary concentration of the minerals or even adopt a cheaper extraction method in order to have an economic balance.

The extraction of manganese appears to be an important sector in hydrometallurgy due to the existence in low-grade ores. These minerals are normally stable in both alkaline and acidic oxidizing conditions. Therefore, the extraction of manganese should be done under reducing conditions. A number of reducing agents, for example, glucose, coal, and biomass have been adopted for the process.

Guillermo Tiburcio Munive and coworkers at the University of Sonora in Mexico undertook a study based on the dissolution of manganese under reducing conditions, which was followed by neutralization with lime, caustic soda, and ammonium chloride to get a pH value of between 8.5-10, as well as leach values of silver and gold with ammonium thiosulfate. Their research work is published in JOM.

The authors used the ore that originates from the mine tailings dams at Hostotipaquillo Jalisco. The solid samples were then analyzed by atomic absorption spectroscopy. The authors analyzed the free acidity, sulfite, and acid consumption through wet process as well as volumetry analyses.

The first stage of the study entailed a reductive acid leaching with sodium sulfite and sulfuric acid to extract manganese. Then the manganese was washed and neutralized with ammonium chloride and calcium chloride. They placed the leached ore from the first phase in contact with ammonium thiosulfate and changing the solid-liquid ratio while assessing the extraction of silver and gold. The authors also evaluated the effect of pH as well as concentration of ammonium thiosulfate.

In the first phase of the experiment, the authors recorded a maximum of 96.05% manganese extraction with a 5:1 liquid to solid ratio. 90.74g/L and 25.8g/L of sulfuric acid and sodium sulfite were used, respectively. The authors recorded an extraction time of 3 h with a head manganese ore of about 3.58%. In the second stage, the authors performed the leaching of silver and gold with ammonium thiosulfate. They recorded a yield of 97.06% and 86.66% for silver and gold, respectively. During this process, sodium thiosulfate consumption was 10.36g/L, which was an economical amount for the head ore with silver and gold content of 310 and 0.3g/ton, respectively.

Moreover, the ore obtained from manganese leaching could be treated with alkali and calcium carbonate in order to neutralize the acidity. Then this could be leached with sodium thiosulfate, sodium cyanide, and ammonium for other industrial applications.